95 E320 Very Rough Running - out of ideas
 

Howdy all,

I've tried to be self-sufficient using this great resource, but have come to the end of my ability to troubleshoot my very rough running 1995 E320. To make matters worse, I'm on the road...850 miles from home, and away from a known good mechanic. Any suggestions on what I should try next would be greatly appreciated.

The problem: Car runs incredibly rough, and barely idles. Power is noticeably reduced. The problem started immediately the other day, and has not gotten better or worse. The engine miss and sputtering is evident at all RPM's and temperatures, although it's a little more pronounced at lower RPM's.

The car had the main wiring harness replaced last year, and has run fine since.

In searching through the forums, I discovered the coil/spark plug boot issue on the M104, and ordered/replaced all three from Phil, along with the plugs. Made no difference.

Next, I built Arthur's Radio Shack code scanner. First time through, I pulled a code #11 on pin 14 ("Closed throttle recognition signal to engine control module"). However, upon clearing the codes, it has yet to return. No other codes on pin 14, and none on pin 3 or 8.

I've looked for vacuum leaks, but not being familiar with the engine, I'm not sure where all to look. There is a two-tone electrical humming noise audible under the hood when the key is on (engine off) that I don't recall being there before, but I'm not certain...it may be normal.

Any thoughts?

MESSAGE ME your vin I will try to help you. I will be sending you pdf documents so you can print them out. I cant really get you accurate info without vin in case you are wondering why I ask for it.

Thanks - PM sent.

Also, left out of original post - car has about 85K on it.

Message sent.Check your email. If that doesnt solve your problem let me know.

Da Nag, the humming noise you hear may be a bad OVP relay located behind the battery. Remove the battery and the black plastic piece to access the OVP relay. It's simple to replace.

It could be a bad coil. Has happened to me twice and the car starts running on 4 cilinders and feels like crap.

It could be a bad ovp, ignition coil but dont send the guy on a wild goose chase.

Running Rough M104
 

Howdy!

I had a 300E 3.2L (1993) that exhibited the same problem once. It was the wiring harness of the engine. It was causing a miss due to the wire harness shell flaking off and allowing the sending and receiving wires to touch. If you have not replaced your wiring harness, i would start there. On the lighter side, it could just be a bad coil. I would remove the cover that houses the spark wires and coils and start swapping around!

Best Of Luck!

Also, for what it's worth, i have seen a failing Mass Airflow Meter do the cause similar problems...

-Mike:)